The present disclosure relates generally switches and, more particularly, to a circuit that drives a motor or other device utilizing parallel IGBT switches.
Insulated-gate bipolar transistors (IGBTs) are well known three-terminal power semiconductor devices. Due to their high efficiency and fast switching they are often used for switches primarily used as an electronic switch and can be used, for example, in inverters that convert a direct current (DC) voltage into an alternating current (AC) voltage.
In some cases a particular IGBT may not, due to thermal constraints, be able to handle the voltage/current required in a particular situation. One approach is to use two IGBTs in parallel to handle higher current. Such an approach would reduce thermal stress effects and add to the modularity of a particular system. In such cases, two parallel connected IGBTs are driven by a common or separate gate drives.
Paralleled IGBTs requires very careful design and layout of the IGBTs and busbars, requires effective heatsink to avoid thermal runaway, and careful design of gate drive to minimize the unequal current sharing during switching as well as steady state. With the prior art direct paralleling technologies, even with carefully lay out busbars and gate drives, it is not easy to achieve close to ideal steady state current sharing. Further, dynamic current sharing during turning-on and turning-off can be much worse.
Newer generations of IGBTs are switching ever faster. This means the dynamic sharing between paralleled IGBTs is getting more challenging, and the capacity utilization of paralleled IGBT is getting worse. For instance, In a six IGBT inverter bridge, the mismatch between current sharing, especially the dynamic sharing, differs between the three phase libs, and differs between upper and lower switches due to physical location differences of each IGBTs. The effective current capacity of the inverter would be dictated by the pair of paralleled IGBTs that has the worst sharing.